[PATCH] Add default parameter to MCSymbol accessors to control IsUsed

[Vedant Kumar via llvm-commits]

Ping

We were discussing "invalid reassignment to non-absolute variable" and whether we still need it around.

thanks
vedant

> On Aug 13, 2015, at 9:31 AM, Vedant Kumar <vsk at apple.com> wrote:
> 
> Hi Rafael,
> 
> Sorry for the delay on this.
> 
>> I think that dates from the early days of MC. My understanding is that
>> it was added just as a safety so that we have to reason about code
>> like
>> 
>> foo = bar
>> .long foo
>> foo = zed
>> .long foo
>> 
>> Should that produce two relocations with bar, two with foo or one each?
> 
> Here is what GAS does:
> 
> SYMBOL TABLE:
> 00000000 l    d  .text	00000000 .text
> 00000000 l    d  .data	00000000 .data
> 00000000 l    d  .bss	00000000 .bss
> 00000000         *UND*	00000000 bar
> 00000000         *UND*	00000000 zed
> 
> RELOCATION RECORDS FOR [.text]:
> OFFSET   TYPE              VALUE 
> 00000000 R_386_32          bar
> 00000004 R_386_32          zed
> 
> Here is a different test that initially triggered this issue:
> 
>> foo = bar
>> .long foo
>> foo = bar
>> .long foo
> 
> 
> And here is GAS's output:
> 
> RELOCATION RECORDS FOR [.text]:
> OFFSET   TYPE              VALUE 
> 00000000 R_386_32          bar
> 00000004 R_386_32          bar
> 
> With the patch I suggested, both of these examples just work with llvm-mc. Here's what the relocation table looks like on Darwin for comparison:
> 
> Relocation information (__TEXT,__text) 2 entries
> address  pcrel length extern type    scattered symbolnum/value
> 00000004 0     2      1      0       0         1
> 00000000 0     2      1      0       0         1
> 
> This looks sane to me. I've updated the patch to get rid of the "invalid reassignment to non-absolute variable" error and fixed the test cases. Could you review it for any issues?
> 
> thanks
> vedant
> 
> <MCSymbol-patch1-NFC.patch><MCSymbol-patch2.patch>